1. Field of the Invention
This invention concerns a process for dynamic channel allocation in mobile radio networks, where priorities are established for the individual channels and are increased or reduced as a function of the interference occurring in the respective channel.
2. Discussion of the Prior Art
In mobile radio networks, transmissions between base stations and mobile stations go over channels that are established by at least one time slot on at least one carrier. In the case of a line-oriented transmission, one of the available channels must be allocated in establishing a connection and in changing from one base station to another. In the case of a package-oriented transmission, a channel must be allocated for each cohesive segment of the link.
Various types of interference that impair the transmission quality can occur in the channels. In addition to interference due to neighboring cells having the same frequencies, interference due to other interference sources can also occur, such as ignition sparks of motor vehicles, atmospheric interference and thermal noise at a low reception field strength. This interference is subject to fluctuations over time that should be taken into account in the channel allocation.
A self-adaptive, learning method of dynamic channel allocation is described by Y. Furuya and Y. Akaiwa, "Channel Segregation, A Distributed Adaptive Channel Allocation Scheme for Mobile Communication Systems," IEICE Transactions, vol. E 74, no. 6, pages 1531 ff. (June 1991), and by Y. Akaiwa and H. Andoh, "Channel Segregation, A Self-Organized Dynamic Channel Allocation Method: Application to TDMA/FDMA Microcellular Systems," IEEE Journal on Selected Areas in Communications, vol. 11, no. 6, pages 949 ff. (August 1993). The algorithm used there is called "Channel Segregation" (CSEG). The known method can be used with package-oriented transmission as well as line-oriented transmission. Each base station maintains a list of priorities for all channels available to it. After each cohesive segment of the link, the list of priorities is incremented if there was no interference in the transmission or is decremented if there was interference. Each time a new channel is allocated, the free channel with the highest priority at the moment is always the one allocated.
Then over a period of time, a pattern of usage develops in the network, where the channels with a high priority are allocated more and more frequently and those with a lower priority are allocated less and less frequently. This pattern of usage is just as static as the so-called Fixed Channel Allocation (FCA), where the available frequency resources are distributed uniformly over a repeating cell structure. This process thus guarantees that the channels will interfere with each other as little as possible with a uniform radio traffic volume. However, this is extremely inefficient when the traffic distribution is not uniform.
An improved method of dynamic channel allocation, based on the algorithm of "Channel Segregation" described above, is described by K. Hamabe, T. Ueda, T. Otsu, "Distributed Adaptive Channel Allocation Scheme with Variable C/I Threshold in Cellular Systems," 43.sup.rd IEEE Vehicular Technology Conference, Meadowlands Hilton, Secaucus, N.J., USA (May 1993). To achieve a more uniform channel allocation, a threshold value is established for the carrier/interference ratio (C/I) and is set lower for channels with a low priority than for channels with a high priority. To do so, the available channels are subdivided into three groups according to priority, where a threshold value is assigned to each group.
This process ensures a more uniform utilization of the capacity of the channels, but it does not react optimally to changes, for example, a change in traffic conditions.